1. Field of the Invention
The present invention relates to a distributed-constant circuit type magnetic field detector for detecting an external magnetic field working on a novel principle and suitable for use, for example, in a magnetic reproducing head which detects a signal magnetic field from a magnetic recording medium such as a magnetic tape, a magnetic disk, and a floppy disk.
2. Description of the Related Art
In reproducing magnetic record recorded on magnetic recording media, ring-shaped inductive magnetic heads utilizing electromagnetic induction have long been used. However, with the recent increase in recording density and operating frequency, various problems are arising.
First, the increase in the recording density is lowering the relative speed between the magnetic reproducing head and the recording medium. Hence, the reproduced output power by the inductive reproducing head is becoming extremely lower.
To cope with this situation, development and practical use of magnetoresistive effect (MR) reproducing heads are being advanced. The MR head is that of a magnetic flux sensitive type not dependent on its relative speed with the magnetic recording medium. Since the reproduced output by it is proportional to the current passed through the MR element, it is expected theoretically that the voltage will become higher the larger the current is. In practice, however, there is an upper limit to it because of heat to be produced by the current flow. On the other hand, since the reproduced output power is proportional also to the MR ratio of the MR element, materials having greater MR ratio are being intensively searched for. At present, Permalloy is being used chiefly, but its reproducing output power is not sufficient because its MR ratio is not higher than 2% or so. Besides, there is a big problem with the MR head that it produces Barkhausen noise to deteriorate the S/N ratio.
As another magnetic reproducing head of a magnetic flux sensitive type, there is proposed a magnetic reproducing head utilizing a change in the resonance characteristic of a coil by an external magnetic field (for example, Preprints for Spring National Conference of the Institute of Electronics, Information and Communication Engineers, 1990, pp. 5-35). However, this proposed head is not adapted to be a distributed-constant circuit and, further, permeability of the magnetic member used therein is in the frequency domain under 1 GHz.
As described above, with the recent rapid increase in the information quantity to be recorded, there are strong demands for higher recording density and higher-frequency performance in magnetic recording. These demands are especially strong in the field of hard disk units as external memory for video equipment and computers. Video equipment is required to support the high-definition television and digital television coming into existence and hard disk units are urged to support the extended scale of software and increased quantity of processed data and so on accompanying improvement in performance of computers. To meet the demands for higher recording density and performance at higher frequency, it is necessary for the magnetic reproducing head to be highly sensitive and excellent in high-frequency characteristics.